Room-temperature-curable (RTC) polyorganosiloxane compositions that comprise hydroxyl-endblocked polyorganosiloxane as base component in combination with a crosslinker bearing silicon-bonded hydrolyzable groups are known in the art. These compositions are widely used as sealants, coatings, electrical insulation, and moldmaking materials. One problem associated with the application of these RTC compositions as, for example, a sealant or coating, has been the loss of aesthetics that occurs due to staining or soiling of the surface of the cured product and its surroundings. As a consequence, various additives have been proposed in order to improve the resistance of these RTC polyorganosiloxane compositions to staining. For example, Japanese Laid Open (Kokai or Unexamined) Patent Application Number Sho 62-1750 (1,750/1987) teaches an RTC polyorganosiloxane composition that contains an ester from an alcohol and an unsaturated higher aliphatic acid. Unfortunately, this ester is poorly compatible with the hydroxyl-endblocked polyorganosiloxane that is the base component of this composition. When such a composition is deployed in a one-package formulation, the ester will undergo phase separation within the container with elapsed time during storage. This results in a deterioration in storage stability and a decline in the anti-staining activity. While deployment as a two-package formulation (e.g. where base component and crosslinker are mixed just before use) does eliminate the problem of phase separation by the ester with elapsed time, with this type of formulation the ester dispersed in the polyorganosiloxane phase rather rapidly separates out in large amounts on the surface of the cured product. This prevents the long-term manifestation of anti-staining activity. Thus, there is a need for an unsaturated higher aliphatic acid ester-based anti-staining additive that is highly compatible with the polyorganosiloxane base component and that manifests an excellent anti-staining activity on a long-term basis.
An object of this invention is to provide an anti-staining additive that is highly compatible with polyorganosiloxanes and that has a long-term ability to inhibit staining of the surface of the cured product and to inhibit staining of substrate in contact with the cured product. An additional object of this invention is to provide a room-temperature-curable polyorganosiloxane composition that contains this anti-staining additive.